Proteins, peptides and other biological molecules (“biological macromolecules”, namely biological polymers such as proteins and polypeptides) are increasingly being use in many diverse areas of science and technology. For example, proteins are employed as active agents in the fields of pharmaceuticals, vaccines and veterinary products. Unfortunately, the use of biological macromolecules as active agents in pharmaceutical compositions is often severely limited by the presence of natural barriers of passage to the location where the active agent is required. Such barriers include the skin, lipid bi-layers, mucosal membranes, severe pH conditions and digestive enzymes.
There are many obstacles to successful oral delivery of biological macromolecules. For example, biological macromolecules are large and are amphipathic in nature. More importantly, the active conformation of many biological macromolecules may be sensitive to a variety of environmental factors, such as temperature, oxidizing agents, pH, freezing, shaking and shear stress. In planning oral delivery systems comprising biological macromolecules as an active agent for drug development, these complex structural and stability factors must be considered. In addition, in general, for medical and therapeutic applications, where a biological macromolecule is being administered to a patient and is expected to perform its natural biological function, delivery vehicles can be used to facilitate absorption through the gastrointestinal tract. These delivery vehicles must be able to release active molecules, at a rate that is consistent with the needs of the particular patient or the disease process.
One specific biological macromolecule, the hormone insulin, contributes to the normal regulation of blood glucose levels through its release by the pancreas, more specifically by the β-cells of a major type of pancreatic tissue (the islets of Langerhans), so that the glucose can be used as a source of energy. Insulin secretion is a regulated process that, in normal subjects, provides stable concentrations of glucose in blood during both fasting and feeding. In normal healthy humans, insulin is secreted from the pancreas into the portal vein, which carries the insulin to the liver. The liver utilizes and/or metabolizes a large portion of the insulin that it receives from the portal circulation.
Blood glucose concentration is the principal stimulus to insulin secretion in healthy humans. Glucose enters the pancreatic β-cell by facilitated transport and is then phosphorylated by glucokinase. Expression of glucokinase is primarily limited to cells and tissues involved in the regulation of glucose metabolism, such as the liver and the pancreatic β-cells. The capacity of sugars to undergo phosphorylation and subsequent glycolysis correlates closely with their ability to stimulate insulin release. It is noted that not all tissues are dependent on insulin for glucose uptake. For example, the brain, kidneys and red blood cells are insulin independent tissues, while the liver, adipose and muscle are insulin dependent tissues.
Diabetes Mellitus (“diabetes”) is a disease state in which the pancreas does not release insulin at levels capable of controlling glucose levels and/or in which muscle, fat and liver cells respond poorly to normal insulin levels because of insulin resistance. Diabetes Mellitus is classified into two types: Type 1 and Type 2. Approximately 5 to 10% of diagnosed cases of diabetes are attributed to Type 1 diabetes, and approximately 90% to 95% to type 2 diabetes.
Type 1 diabetes is diabetes that is insulin dependent and usually first appears in young people. In Type 1 diabetes, the islet cells of the pancreas stop producing insulin mainly due to autoimmune destruction and the patient must inject himself with the missing hormone.
Type 2 diabetes is non-insulin dependent diabetes, which may be caused by a combination of insulin resistance (or decreased insulin sensitivity) and, in later stages, insufficient insulin secretion. This is the most common type of diabetes in the Western world. Close to 8% of the adult population of various countries around the world, including the United States, have Type 2 diabetes, and about 30% of these patients will need to use exogenous insulin at some point during their life spans due to secondary pancreas exhaustion and the eventual cessation of insulin production.
Insulin resistance (or decreased insulin sensitivity) is also prevalent in the population, especially in overweight individuals, in those with risk of diabetes (i.e., pre-diabetic, wherein blood glucose levels are higher than normal but not yet high enough to be diagnosed as diabetes) and in individuals with type 2 diabetes who produce enough insulin but whose tissues have a diminished ability to adequately respond to the action of insulin. In order to compensate and overcome the insulin resistance, the pancreatic β-cells initially increase their insulin production such that insulin resistant individuals have high plasma insulin levels. However, after a period of high demand placed on these cells, the cells start to decompensate and exhaust, and insulin secretion is reduced at later stages of diabetes. By the time an individual is diagnosed with type 2 diabetes, roughly 50% of the β-cells have died due to increased demand for insulin production.
Diabetes is the sixth leading cause of death in the United States and accounted for more than 193,000 deaths in 1997. However, this is an underestimate because complications resulting from diabetes are a major cause of morbidity in the population. Diabetes is associated with considerable morbidity and mortality in the form of cardiovascular disease, stroke, digestive diseases, infection, metabolic complications, ophthalmic disorders, neuropathy, kidney disease and failure, peripheral vascular disease, ulcerations and amputations, oral complications, and depression. Thus, diabetes contributes to substantially many deaths that are ultimately ascribed to other causes.
The main cause of mortality with Diabetes Mellitus is long term micro- and macro-vascular disease. Cardiovascular disease is responsible for up to 80% of the deaths of type 2 diabetic patients, and diabetics have a two- to four-fold increase in the risk of coronary artery disease, equal that of patients who have survived a stroke or myocardial infarction. In other words, heart disease, high blood pressure, heart attacks and strokes occur two to four times more frequently in adult diabetics than in adult non-diabetics. This increased risk of coronary artery disease combined with an increase in hypertensive cardiomyopathy manifests itself in an increase in the risk of congestive heart failure. These vascular complications lead to neuropathies, retinopathies and peripheral vascular disease.
Diabetic retinopathy (the breakdown of the lining at the back of the eye) is the leading cause of blindness in adults aged 20 through 74 years, and diabetic kidney disease, e.g., nephropathy (the inability of the kidney to properly filter body toxins), accounts for 40% of all new cases of end-stage renal disease (kidney failure). Furthermore, diabetes is also the leading cause for amputation of limbs in the United States. Diabetes causes special problems during pregnancy, and the rate of congenital malformations can be five times higher in the children of women with diabetes.
Insulin resistance plays an important role in the pathogenesis of hyperglycemia in type 2 diabetes, which eventually induces the development of diabetic complications. Furthermore, insulin resistance ostensibly plays a role in the pathogenesis of macrovascular disease, cardiovascular diseases and microvascular disease.
Poor glycemic control contributes to the high incidence of these complications, and the beneficial effects of tight glycemic control on the chronic complications of diabetes are widely accepted in clinical practice. However, only recently has it been firmly established that elevated blood glucose levels are a direct cause of long-term complications of diabetes. The Diabetes Control and Complications Trial and the United Kingdom Prospective Diabetes Study both showed that control of blood glucose at levels as close to normal as possible prevents and retards development of diabetic retinopathy, nephropathy, neuropathy and microvascular disease.
In type 1 diabetes, insulin therapy is essential and is intended to replace the absent endogenous insulin with an exogenous insulin supply. In type 2 diabetes, therapy has consisted of oral antidiabetic agents, which increase insulin sensitivity and/or insulin secretion, and insulin if, and when, the oral agents fail.
The problem of providing bioavailable unmodified human insulin, in a useful form, to the ever-increasing population of diabetics has occupied physicians and scientists for almost 100 years. Many attempts have been made to solve some of the problems of stability and biological delivery of this peptide. Because insulin is a peptide drug (MW approx. 6000 Da) that is not absorbed in the gastrointestinal tract, it ordinarily requires parenteral administration such as by subcutaneous injection. Thus, most diabetic patients self-administer insulin by subcutaneous injections, often multiple times per day. However, the limitations of multiple daily injections, such as inconvenience, poor patient acceptability, compliance and the difficulty of matching postprandial insulin availability to postprandial requirements, are some of the better-known shortcomings of insulin therapy.
Despite studies demonstrating the beneficial effects of tight glycemic control on chronic complications of diabetes, clinicians are not particularly keen on aggressive insulin therapy, particularly in the early stages of the disease, and this is widely accepted in clinical practice. The unmet challenge of achieving tight glycemic control is due, in part, to the shortcomings of the available subcutaneous route of insulin administration and the fear of hypoglycemia. In addition to the practical limitations of multiple daily injections discussed above, the shortcomings of the commonly available subcutaneous route of insulin administration have resulted in the generally inadequate glycemic control believed to be associated with many of the chronic complications (comorbidities) associated with diabetes.
Hyperinsulinemia (elevated blood concentrations of insulin) can occur by the administration of insulin in a location (and manner) that is not consistent with the normal physiological route of delivery. Insulin circulates in blood as the free monomer, and its volume of distribution approximates the volume of extracellular fluid. Under fasting conditions, the concentration of insulin in portal blood is, e.g., about 2-4 ng/mL, whereas the systemic (peripheral) concentration of insulin is, e.g., about 0.5 ng/mL, in normal healthy humans, translating into, e.g., a 5:1 ratio. In human diabetics who receive insulin via subcutaneous injection, the ratio is changed to about 0.75:1. Thus, in such diabetic patients, the liver does not receive the necessary concentrations of insulin to adequately control blood glucose. Elevated systemic levels of insulin may lead to increased glucose uptake, glycogen synthesis, glycolysis, fatty acid synthesis, cortisol synthesis and triacylglycerol synthesis, leading to the expression of key genes that result in greater utilization of glucose.
In the field of insulin delivery, where multiple repeated administrations are required on a daily basis throughout the patient's life, it is desirable to create compositions of insulin that do not alter physiological clinical activity and that do not require injections. Oral delivery of insulin is a particularly desirable route of administration, for safety and convenience considerations, because it can minimize or eliminate the discomfort that often attends repeated hypodermic injections. It has been a significant unmet goal in the art to imitate normal insulin levels in the portal and systemic circulation via oral administration of insulin.
Oral delivery of insulin may have advantages beyond convenience, acceptance and compliance issues. Insulin absorbed in the gastrointestinal tract mimics the physiology of insulin secreted by the pancreas because both are released into the portal vein and carried directly to the liver before being delivered into the peripheral circulation. Absorption into the portal circulation maintains a peripheral-portal insulin gradient that regulates insulin secretion. In its first passage through the liver, roughly 60% of the insulin is retained and metabolized, thereby reducing the incidence of peripheral hyperinsulinemia, a factor linked to complications in diabetes. A not uncommon, and serious, complication of insulin treatment and other oral antidiabetic agents is hypoglycemia.
However, insulin exemplifies the problems confronted in the art in designing an effective oral drug delivery system for biological macromolecules. Insulin absorption in the gastrointestinal tract is prevented presumably by its molecular size and its susceptibility for enzymatic degradation. The physicochemical properties of insulin and its susceptibility to enzymatic digestion have precluded the design of a commercially viable oral or alternate delivery system.
Emisphere Technologies, Inc. has developed compositions of insulin that are orally administrable, e.g., absorbed from the gastrointestinal tract in adequate concentrations, such that the insulin is bioavailable and bioactive following oral administration and provide sufficient absorption and pharmacokinetic/pharmacodynamic properties to provide the desired therapeutic effect, i.e., cause a reduction of blood glucose, as disclosed in U.S. patent applications Ser. Nos. 10/237,138, 60/346,746, 60/347,312, 60/368,617, 60/374,979, 60/389,364, 60/438,195, 60/438,451, 60/438,444, 60/452,660 and 60/488,465, as well as in International Patent Application Publications Nos. WO 03/057170, WO 03/057650 and WO02/02509, all assigned to Emisphere Technologies, Inc., all of which are incorporated herein by reference.
The novel drug delivery technology of Emisphere Technologies, Inc. is based upon the design and synthesis of low molecular weight compounds called “delivery agents.” When formulated with insulin, the delivery agent, which is in a preferred embodiment 4-CNAB (sodium N-[4-(4-chloro-2 hydroxybenzoyl)amino]butyrate) enables the gastrointestinal absorption of insulin. It is believed that the mechanism of this process is that 4-CNAB interacts with insulin non-covalently, creating more favorable physical-chemical properties for absorption. Once across the gastrointestinal wall, insulin disassociates rapidly from 4-CNAB and reverts to its normal, pharmacologically active state. 4-CNAB is not intended to possess any inherent pharmacological activity and serves only to increase the oral bioavailability of insulin by facilitating the transport of insulin across the gastrointestinal wall. The pharmacology of insulin is the desired therapeutic effect and is well characterized.
Whereas traditional subcutaneous insulin dosing shifts the point of entry of insulin into the circulation from the natural site (the portal vein) to the systemic circulation, the oral dosing method developed by Emisphere Technologies, Inc. mimics natural physiology, namely, the ratio of concentration of unmodified insulin in the portal circulation to that in the systemic circulation approaches the normal physiological ratio, e.g., from about 2:1 to about 6:1. The effect of this route of dosing is two fold. First, by targeting the liver directly, a greater control of glucose may be achieved. Various studies have shown that intraportal delivery of insulin can yield a comparable control of glucose at infusion rates lower than those required by peripheral administration. Because the insulin will undergo substantial (˜50%) first-pass metabolism prior to entering the systemic circulation, a lower serum concentration and total exposure is achieved. This may, in turn, alleviate any detrimental effects of insulin on non-target tissues.
Insulin/4-CNAB capsules were evaluated by Emisphere Technologies, Inc. in a nonclinical program that included pharmacological screening, pharmacokinetic and metabolic profiles, and toxicity assessments in rats and monkeys. These studies in rats and monkeys showed that 4-CNAB is absorbed rapidly following oral administration.
Insulin/4-CNAB capsules were also evaluated by Emisphere Technologies, Inc. in clinical studies for the safety, pharmacokinetics, pharmacodynamics, and the effect of food on the absorption of insulin. In these studies, 4-CNAB was shown to enhance the gastrointestinal absorption of insulin following oral administration in diabetic patients and healthy subjects. Oral administration of Insulin/4-CNAB capsules resulted in rapid absorption of both insulin and 4-CNAB, and the insulin absorbed orally in combination with 4-CNAB was pharmacologically active, as demonstrated by a reduction of blood glucose in healthy and diabetic subjects and by a blunting of postprandial glucose excursion in diabetic patients. These studies suggest that oral administration of a formulation of insulin/4-CNAB is well-tolerated and reduces blood glucose concentrations in both healthy subjects and diabetic patients.
In normal physiology, first-phase insulin secretion takes place 5 to 20 minutes after the start of a meal, and this effect has a well-known impact on prandial glucose homeostasis. The loss of first-phase insulin secretion is a characteristic feature of Type 2 diabetic patients in the early stages of the disease, and it is also observed in prediabetic states, namely individuals with impaired glucose tolerance. In the absence of first-phase insulin secretion, the stimulatory effect of glucagon on gluconeogenesis is not suppressed and may contribute to the development of prandial hyperglycemia. In the basal state as well as in the prandial phase, plasma glucose concentrations are correlated with hepatic glucose output. Therefore, restoration of first-phase insulin secretion at the time of meal ingestion should suppress prandial hepatic glucose output and subsequently improve the blood glucose profile.
Several approaches have been undertaken to prove this hypothesis. However, the therapeutic regimens were either too dangerous for a long-term treatment (such as intravenous administration of regular human insulin) or pharmacologically unsuitable (fast-acting insulin analogues). Furthermore, restoration of first phase insulin response appears to be difficult in patients with a long-standing history of diabetes who have lost most or all of their endogenous insulin secretion capacity.
Currently, regular subcutaneously injected insulin is recommended to be dosed at 30 to 45 minutes prior to mealtime. As a result, diabetic patients and other insulin users must engage in considerable planning of their meals and of their insulin administrations relative to their meals. Unfortunately, intervening events that may take place between administration of insulin and ingestion of the meal may affect the anticipated glucose excursion. Furthermore, there is also the potential for hypoglycemia if the administered insulin provides a therapeutic effect over too great a time, e.g., after the rise in glucose levels that occur as a result of ingestion of the meal has already been lowered.
In addition, certain short acting insulin formulations, because of the speed with which the insulin provides a blood glucose lowering effect, may, between the time of administration of insulin and the time of ingestion of the meal, contribute to a lowering of blood glucose to a level that could range from subclinical hypoglycemia to more undesirable effects.
It is desirable to provide an oral insulin treatment for early phase and late phase diabetic patients, and for individuals with impaired glucose tolerance who have impaired first phase insulin secretion, which treatment can be administered orally at or shortly prior to mealtime and that has a short duration of action.